Flat panel displays such as liquid crystal display (LCD) and plasma types are typically used in consumer electronics devices such as desktop computers, television sets, and portable devices such as smart phones, tablet computers, and notebook computers. Such a flat panel display contains an array of display elements or pixels that are formed on a display panel substrate that is made of substantially transparent materials including one or more glass panels. The array of display elements may be overlaid with a grid of data and control conductors, referred to as data lines and gate lines that are also formed on the display panel. In a high-resolution panel, there may be tens of thousands of pixels where each is to receive a signal that represents a digital picture element to be displayed at that location. The picture element signals together with control signals are applied to the conductive grid of gate lines and data lines by a display driver integrated circuitry (some times referred to as a display driver or source driver integrated circuit, IC, or simply a driver IC). The driver IC may be a microelectronic semiconductor die that contains the needed circuitry to translate incoming video and touch transducer signals for example from an external video/graphics/touch controller, into the data and control signals for driving the pixel array. The driver IC may also receive other control signals as well as power, from an external power supply circuit, for example as part of a power management unit integrated circuit.
The external circuitry is electrically connected to the driver IC via conductive traces that may also be formed in the display panel substrate, while some of the external circuitry may be off-the-panel and accessible via for example a flexible carrier circuit. As a result, to transfer the electrical signals and power between the driver IC and external circuitry, there is a need for a reliable and low impedance electrical interconnect between the driver IC and the conductive traces that are formed in the display panel substrate. For example, a chip-to-substrate (CoG) joint is typically made between a pad of the driver IC and a counterpart pad or trace formed in the display panel substrate. Sometimes, flip chip interconnect technologies are also used to achieve hundreds of such CoG joints. Low cost techniques used to form such joints include conductive adhesive film, which do not always provide for a well-controlled or narrow range of low resistance, across a large number of such joints. As a result, there is a need to measure the electrical resistance of such joints particularly during manufacturing testing, so as to be able to screen out those parts that are outside a specified resistance range. That is, a display system that has a large number non-conforming CoG joints (greater than a specified resistance) may result in greater power consumption and/or slower signal transitions, thereby potentially causing functional failures in the display system.